The molecular mechanisms of transduction in cone photoreceptors of the vertebrate retina will be investigated. Specifically two aspects of these mechanisms will be studied: 1) the role of Ca ion and 2) the properties of both light dependent and light insensitive ionic channels in the cone plasma membrane. The possible role of Ca ions will be studied by investigating the physiological consequences of buffering changes in intracellular Ca concentration and by attempting to measure light-induced changes in the concentration of Ca ions both in the space immediately outside the cone outer segment and in its intracellular space. The ionic channels of the cone plasma membrane will be studied with patch electrodes. At first the macroscopic ionic currents flowing through these channels will be determined and this will serve as the basis to identify individual channels. Each individual channel type will be investigated to determine its kinetics, current-voltage characteristics and ion selectivity.